This invention relates generally to analytical testing apparatus and the like, and more specifically relates to devices useful in the sampling of gases from hydrocarbon cracking furnaces.
During the operation of hydrocarbon cracking plants and systems, it is necessary to continually withdraw samples of the pyrolysis gases from points downstream of the hydrocarbon cracking furnaces, in order to perform important, if not essential, analytical determinations with respect to the said gases. Thus, for example, it is desirable to continually provide these gases to on-stream process analyzers or the like, in order to establish such important data as the yields of a given hydrocarbon fraction. Further, it may be desired to determine various ratios of gaseous components in the said samples, in order in turn to establish the efficiency with which the cracking system is operating.
In order to carry out the aforementioned operations, the gases which are withdrawn downstream of the cracking furnace, are normally subjected to conditioning apparatus, the purpose of which is to separate from the gross mixture of withdrawn gases, the particular hydrocarbon fraction or fractions which are of interest for furnishing to the analytical instrumentation. In addition to performing a separation of the desired hydrocarbon fractions, particulate matter and the like which may be entrained in the gaseous mixture should be removed, and in other respects the sample rendered at a relatively uniform temperature so that the separated fraction will not vary or change, whereby the results of analysis will be consistent from sample to sample.
In the past, various techniques and apparatus configurations have been utilized for the aforementioned sampling purposes. In one very simple approach, for example, a tube within a tube was inserted into a nozzle in a transfer line proceeding from the cracking furnace. The inner tube contained cold or hot water or steam which continuously poured into the transfer line while gas from the transfer line moved up the outer tube. This technique, however, was extremely troublesome, and required extensive maintenance to keep the sample point operational.
More recently, apparatus has been utilized which improved upon the aforementioned prior art, by employing an internal reflux condenser which is mounted on top of the transfer line, normally in a vertical position but, in some instances, at an angle up to 45.degree.. The internal reflux condenser consists of two sections--a lower packed reflux filter section, and an upper condenser section. Condensables formed in the upper section dropped to the lower reflux section tending to maintain the reflux section in relatively clean condition to limit maintenance requirements. This type of apparatus has been found to provide a relatively good and reliable sample of C.sub.4 and lighter hydrocarbons saturated with C.sub.5 's and traces of C.sub.6 's and heavier fractions. The said apparatus is not, however, practical for use in separating heavier hydrocarbon fraction samples.
In accordance with the foregoing, it may be regarded as an object of the present invention, to provide a gas sample conditioning apparatus adapted for receiving pyrolysis gases from a hydrocarbon cracking furnace, and providing a conditioned gas sample for on-stream process analyzers or the like.
It is a further object of the invention, to provide apparatus of the above character, which is suitable for use in providing conditioned gas samples from a C.sub.8 fraction down (i.e. to lower chain length fractions).
It is a yet further object of the invention, to provide apparatus of the foregoing character, which enables sampling from an ethylene or other hydrocarbon cracking furnace transfer line or the like, which operates for long periods without plugging, which maintains a carefully controlled temperature gradient in lower portions of the apparatus in order to achieve accurate separation, and which provides a highly uniform temperature in the sample provided from the said apparatus for testing purposes, thereby assuring relatively maintenance-free operation and good reproduceability of results.